1. Field of the Invention
The present invention relates to transport devices of the type useable in a recorder for moving a continuous paper web past a recording head in a straight path with substantially uniform tension.
2. Description of the Prior Art
A paper transport device for use in a recorder is known from German Pat. No. 20 10 019 which has a support means for the clean paper, rollers for guiding the paper, and a motor-driven means for moving the paper from the support means across a writing surface at which a recording means is disposed. In this conventional device, the means for actually moving the paper web is a turning roller which is driven by the motor and which has an idler roller associated therewith which, viewed in the forward feed direction of the paper web, engage one lateral edge of the paper web. Under certain conditions, this single-sided pull on the paper web may, particularly in the case of longer paper transport paths, cause the paper web to no longer be conveyed by the transport means in a straight line. Such skewing of the paper web causes curves and other data recorded on the paper web to become distorted.
One attempted solution to the skewing problem which is present in such conventional devices in the use of a pivotable turning roller by means of which the paper is always returned to the proper straight position. This attempted solution, however, operates satisfactorily only in combination with a paper web of a certain width, and when the width of the paper web exceeds this limitation, the single-sided pull on the paper still causes skewing of the paper web.
Another paper transport device is known from Siemens Prospectus ME 1114/5562.101, 1979 (the "Mingograf 34") in which the drive roller and the idler roller are disposed in the center of the paper web so that a symmetrical tension is exerted on the web. This structure, however, reduces the amount of paper width which is useable for recording or plotting due to the disposition of the idler roller in the center of the paper web. If the recording fluid has not yet completely dried when passing the rollers, the recording channel in the area of the rollers cannot generally be exploited.